Raúl González

Argentinian coastal waters: A temperate habitat for three species of threatened sea turtles

Abstract Three out of the five threatened species of sea turtle occurring in the SW Atlantic Ocean are regularly found in the coastal waters of Argentina: green (Chelonia mydas), loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) turtles. From 1995 to 2008, fishery and beach surveys were carried out along 2800 km coastline and reports from the public were gathered. Incidental capture in artisanal fisheries and strandings suggest that an important concentration of these species occurs in the estuarine, highly productive areas of Samborombón Bay (35°30′S–36°30′S) and El Rincón (39°S–41°S), although green and loggerhead turtles were also recorded as far south as northern Patagonian waters (42°35′S–64°17′W). Depending on the species, different age classes use these temperate areas probably as foraging grounds: small juvenile green turtles, juvenile to adult loggerheads and adult leatherbacks. All three species are mainly captured in small-scale, gillnet fisheries. This information provides an essential background to conduct further studies and propose mitigation plans to reduce sea turtle mortality in Argentina. Global conservation strategies will also benefit from including temperate environments of the SW Atlantic Ocean as regular habitats in the life history of threatened turtles.

Comparison of AVHRR and SeaWiFS imagery with fishing activity and in situ data in San Matías Gulf, Argentina

Seven years (January 2000 to December 2006) of AVHRR and SeaWiFS data were used to estimate monthly climatological means and to present SST and chlorophyll-a seasonal evolution in San Matías Gulf, located between 40° 47′ S and 42° 13′ S on the Argentine coast. SST and chlorophyll-a satellite maps corresponding to spring–summer showed two well differentiable sectors: the southern zone presented colder waters and higher chlorophyll-a concentration while the northern one showed warm water and lower chlorophyll-a. Hake (Merluccius hubbsi) is the most important resource in terms of landings and economic revenues of the San Matías Gulf. Fishing activity data gathered by a Vessel Monitoring System (2004–2006) were linked with SST and chlorophyll-a maps showing that the fishing vessels operated on the thermal front from November to March and had the maximum hake yields. In addition, AVHRR-SST and SeaWiFS-chlorophyll-a data were compared with temperature and chlorophyll-a measured in oceanographic surveys carried out in 2007.

Spatial patterns of the Argentine hake Merluccius hubbsi and oceanographic processes in a semi-enclosed Patagonian ecosystem

Abstract Time-series of fishing position, landings, satellite-derived sea-surface temperature and chlorophyll a concentrations were used to relate the spatial–temporal distribution of the Argentine hake Merluccius hubbsi with seasonal oceanographic processes in San Matías Gulf. Also, the seasonal effect of fishing on the hake population structure was analysed. During summer the fleet was concentrated over the area of the frontal system, obtaining the best catch-per-unit-effort (CPUE) of hake in relatively deep waters. In autumn, the dispersion of the fleet due to a reduction in CPUE coincided with the dissipation of the front, suggesting that the distribution and shoaling of the Argentine hake is associated with seasonal thermal structures. In spring, the thermal structure of the waters and the chlorophyll a blooms seem to modulate the timing of spawning of hake, which occurs mainly in October–November. In addition, the fleet captured a higher proportion of females in the gonadal recovery stage during warm months (November–April). While winter catches (May–October) consisted mainly of males, the intense summer fishing may result in a high impact on the female population. This information is relevant to design of spatial management tools intended to provide biological sustainability to the hake fishery.

Feeding strategy and cannibalism of the Argentine hake Merluccius hubbsi

The diet composition and feeding strategy of the Argentine hake Merluccius hubbsi in the San Matías Gulf were analysed in order to use this information for the sustainable management of the fishery. Merluccius hubbsi behaved as an opportunistic predator. Small M. hubbsi consumed planktonic crustaceans, whereas medium and large fish ate numerous prey taxa with low frequency of occurrence and variable specific abundance. Intra- and intercohort cannibalism were detected in all size groups and were particularly significant in large M. hubbsi. Medium-sized M. hubbsi consumed small conspecifics and large-sized M. hubbsi consumed both small and medium M. hubbsi. These results indicate that the removal of large M. hubbsi by fishing may increase the risk of overfishing by two combined effects: a direct effect of recruitment-overfishing and an indirect effect of growth-overfishing through an enhanced cannibalism of medium M. hubbsi on small M. hubbsi. Intra- and intercohort cannibalism and other trophic relationships in the M. hubbsi should therefore be considered explicitly in stock assessment models.

When Conventional Fisheries Management Fails to Reduce the Catch and Discard of Juvenile Fish: A Case Study of the Argentine Hake Trawl Fishery in San Matías Gulf

Abstract The performance of management measures adopted to reduce the catch of small-size fish in trawl fisheries requires a proper evaluation taking into account that different factors (e.g., the behavior of fishermen, gear efficiency, market forces, and weak controls) may affect the results. The high bycatch of juvenile Argentine hake Merluccius hubbsi recorded in the trawl fishery of San Matias Gulf, Argentina, could be an indication of a suboptimal harvesting pattern that should be addressed. Regulations to mitigate this problem (i.e., a minimum mesh size and the seasonal closure of a nursery area) were imposed in 1997–1998. The purpose of this study was to assess the efficacy of the size-selectivity measure 10 years after its implementation based on two key indicators: the presence of juvenile Argentine hake in catches and discard rates. Our results show that this measure was ineffective in reducing the catch and discard of juveniles and that both indicator values increased during the period analyzed...

Reproductive traits of the small Patagonian octopus Octopus tehuelchus

This study evaluated the reproductive features of Octopus tehuelchus in three coastal environments of San Matías Gulf (Patagonia). Monthly samples of O. tehuelchus were used to estimate size at maturity, compare seasonal changes in oocyte size frequency distributions between sites as well as oocyte number and size between female maturity stage and sites. Females in Islote Lobos had a smaller size at maturity than females in San Antonio Bay and El Fuerte, probably as a consequence of a generally smaller body size. Males in San Antonio Bay were smaller at maturity than females. O. tehuelchus is a simultaneous terminal spawner. Fecundity (expressed as number of vitellogenic oocytes in ovary) was lower in Islote Lobos, and an increase in oocyte number in relation to female total weight was found. Females in San Antonio Bay had the largest oocytes, which may indicate higher energy reserves for the embryo and therefore higher juvenile survival. There was a close relationship between reproduction, growth and condition, represented as size at maturity, number and size of vitellogenic oocytes and period of maturity and spawning. Given the local variation in some reproductive features of O. tehuelchus, studies should focus on the environmental factors, which bring about this variation, and on how it affects the dynamics of local populations.

Genetic evidence and new morphometric data as essential tools to identify the Patagonian seahorse Hippocampus patagonicus (Pisces, Syngnathidae).

A genetic study to support morphometric analyses was used to improve the description and validate the Patagonian seahorse Hippocampus patagonicus (Syngnathidae) on the basis of a large number of specimens collected in the type locality (San Antonio Bay, Patagonia, Argentina). DNA sequence data (from the cytochrome b region of the mitochondrial genome) were used to differentiate this species from its relatives cited for the west Atlantic Ocean. Both phylogenetic and genetic distance analyses supported the hypothesis that H. patagonicus is a species clearly differentiated from others, in agreement with morphometric studies. Hippocampus patagonicus can be distinguished from Hippocampus erectus by the combination of the following morphometric characteristics: (1) in both sexes and all sizes of H. patagonicus, the snout length is always less than the postorbital length, whereas the snout length of H. erectus is not shorter than the postorbital length in the largest specimens; (2) in both sexes of H. patagonicus, the trunk length:total length (LTr :LT ) is lower than in H. erectus (in female H. patagonicus: 0·27-0·39, H. erectus: 0·36-0·40 and in male H. patagonicus: 0·24-0·34, H. erectus: 0·33-0·43) and (3) in both sexes, tail length:total length (LTa :LT ) in H. patagonicus is larger than in H. erectus (0·61-0·78 v. 0·54-0·64).

Environmental Niche Overlap between Common and Dusky Dolphins in North Patagonia, Argentina

Research on the ecology of sympatric dolphins has increased worldwide in recent decades. However, many dolphin associations such as that between common dolphins (Delphinus delphis) and dusky dolphins (Lagenorhynchus obscurus) are poorly understood. The present study was conducted in the San Matías Gulf (SMG) ecosystem (North Patagonia, Argentina) where a high diet overlap among both species was found. The main objective of the present work was to explore the niche overlap of common and dusky dolphins in the habitat and temporal dimensions. The specific aims were (a) to evaluate the habitat use strategies of both species through a comparison of their group attributes (social composition, size and activity), and (b) to evaluate their habitat preferences and habitat overlap through Environmental Niche modeling considering two oceanographic seasons. To accomplish these aims, we used a historic database of opportunistic and systematic records collected from 1983 to 2011. Common and dusky dolphins exhibited similar patterns of group size (from less than 10 to more than 100 individuals), activity (both species use the area to feed, nurse, and copulate), and composition (adults, juveniles, and mothers with calves were observed for both species). Also, both species were observed travelling and feeding in mixed-species groups. Specific overlap indices were higher for common dolphins than for dusky dolphins, but all indices were low, suggesting that they are mainly segregated in the habitat dimension. In the case of common dolphins, the best habitats were located in the northwest of the gulf far from the coast. In the warm season they prefer areas with temperate sea surface and in the cold season they prefer areas with relatively high variability of sea surface temperature. Meanwhile, dusky dolphins prefer areas with steep slopes close to the coast in the southwestern sector of the gulf in both seasons.

Short term impact of artisanal dredges in a Patagonian mussel fishery: Comparisons with commercial diving and control sites

Mussels in the San Matías Gulf fishery are targeted using artisanal dredges and diving. The main objective of this study was to assess the direct impact of artisanal dredging on the biota and sediments, and to compare the composition of the catches and the individual damage induced by fishing between dredging and commercial diving. The experimental design included samplings from dredge catches, dredge tracks, control sites and commercial diving. According to their damage level, individuals were scored as undamaged, lightly damaged and severely damaged. Sediment characteristics were analyzed using coring samples and traps. Damage of mussels, mostly corresponding to the severely damaged category, was less than 5% both in samples from dredging and diving. Conversely, mean damage of the main bycatch species (sea urchins and ophiuroids) was 75 and 65% in samples from dredging and diving respectively, being most of the individuals lightly damaged. Considering also the catch sample composition of both fishing methods, dredging affected relatively more individuals than diving. Although sediment removal in dredged areas was three times higher than that in non-dredged ones, mean grain size and gravel percentage of sea floor sediments showed subtle differences between them.

FIRST STUDIES ON MORPHOMETRIC RELATIONSHIPS AND SIZE AT MATURITY OF THE RED CRAB PLATYXANTHUS PATAGONICUS (MILNE-EDWARDS) AND VARIATIONS CAUSED BY RHIZOCEPHALAN INFESTATION, IN THE SAN MATIAS GULF, PATAGONIA, ARGENTINA

Abstract The size at onset sexual maturity in brachyurans can be evaluated considering different criteria, including growth allometry, gonad development stages, and presence of sperm in spermathecas or eggs in the abdomen. Morphometric aspects of males and the presence of eggs in females of P. patagonicus from the northern San Matías Gulf were respectively analyzed to determine its size at onset of the sexual maturity. Crab samples were obtained during a fishing experiment with traps (cubical, pyramidal, and conical, of similar internal volume), performed in the gulf during winter 2005. Also, the parasitism by a sacculinid rhizocephalan was analyzed to discuss possible effects on the reproductive success. All crabs caught were sorted by sex, carapace width (CW) and total weight (TW). Size frequency distributions were compared among sexes. Proportion of females bearing eggs were grouped into 16 size intervals of 5 mm to determine the size of first reproductive maturity based on a criterion of L50%. In males, the allometric change of chela length was analyzed for this purpose. Only individuals exceeding 50 mm were caught. Of 807 crabs caught, 36% (289) were males and 64% (518) were females. The size frequency distributions differed significantly between sexes with males larger than females (K-S test). Relationships of total weight (TW) to carapace width (CW) were calculated for all reproductive types and compared by ANCOVA with the following results: parasitized crabs < females < females with eggs = males. The mean size at first maturity of females was estimated to be 87.66 mm. Size at maturity for male crabs could not be determined from morphometric data because there was no significant difference in the relationship of chela length and CW for juvenile and adult males. All parasitized crabs (73) were females, whose mean width and mean weight were significantly lower than those from nonparasitized individuals. Prevalence was 9% and the mean intensity was one parasite per host. The parasitized crabs resembled juveniles. The size at first maturity and the reproductive capacity of P. patagonicus could be affected by presence of the parasite, even producing significant interference at the population level. Parasitism by sacculinid must be monitored after the starting of an emerging fishery to assess the actual contribution of the reproductive stock.